Optical modules including focal length adjustment and fabrication of the optical modules

ABSTRACT

Fabricating optical devices can include mounting a plurality of singulated lens systems over a substrate, adjusting a thickness of the substrate below at least some of the lens systems to provide respective focal length corrections for the lens systems, and subsequently separating the substrate into a plurality of optical modules, each of which includes one of the lens systems mounted over a portion of the substrate. Adjusting a thickness of the substrate can include, for example, micro-machining the substrate to form respective holes below at least some of the lens systems or adding one or more layers below at least some of the lens systems so as to correct for variations in the focal lengths of the lens systems.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation under 35 U.S.C. §120 of U.S.application Ser. No. 14/064,550, filed on Oct. 28, 2013, which claimsthe benefit of priority of U.S. Provisional Patent Application Nos.61/721,747, filed on Nov. 2, 2012, and 61/772,073, filed on Mar. 4,2013. The entire contents of each of the aforementioned applications areherein incorporated by reference in their entirety.

FIELD OF THE DISCLOSURE

This disclosure relates to optical modules for cameras and otherdevices. It also relates to methods of manufacturing such modules usingwafer-scale manufacturing steps.

BACKGROUND

During the manufacture of devices, in particular optical devices,manufacturing irregularities or manufacturing deviations may occur, forexample, because of more or less unavoidable variations or inaccuraciesin one or more of the process steps. For example, when the opticaldevice includes one or more lens elements, a multitude of such lenselements on a wafer (referred to as an optics wafer) typically wouldhave slightly varying focal lengths despite having the same nominalfocal length. In some cases, the focal length may correspond to theflange focal length (FFL), which refers to the distance between the lastphysical plane of the device (i.e., the physical plane of device that isclosest to sensor) and the focal plane of the device's lens system. Moregenerally, the focal length may refer to any focal length parameter(e.g., the effective focal length (EFL)). In any event, variations inthe focal lengths can result in the focal plane of the lens system lyingoff the image sensor plane, which can lead to inferior image quality.

SUMMARY

The present disclosure describes optical devices and methods offabricating the optical devices. Various approaches are described toprovide focal length adjustments for the lens systems to correct forvariations in the focal lengths of the lens systems.

For example, in one aspect, a method of fabricating optical devicesincludes mounting a plurality of singulated lens systems over asubstrate, adjusting a thickness of the substrate below at least some ofthe lens systems to provide respective focal length corrections for thelens systems, and subsequently separating the substrate into a pluralityof optical modules, each of which includes one of the lens systemsmounted over a portion of the substrate. In some implementations,adjusting a thickness of the substrate can include micro-machining toform respective holes below at least some of the lens systems so as tocorrect for variations in the focal lengths of the lens systems. In someimplementations, adjusting a thickness of the substrate can includesadding one or more layers below at least some of the lens systems so asto correct for variations in the focal lengths of the lens systems.

In another aspect, a method of fabricating optical devices includesplacing a plurality of individual lens stacks on a substrate,micro-machining the substrate at positions below one or more of the lensstacks to adjust focal lengths for the lens stacks, and subsequentlydicing the substrate into a plurality of optical modules, each of whichincludes one or more of the lens stacks on respective portions of thesubstrate.

The described fabrication techniques can be advantageous in someimplementations because they allows the individual lens systems to betested prior to being mounted on a flange focal length (FFL) correctionsubstrate. Such testing allows only those lens stacks that satisfyspecified requirements (e.g., pass the optical or other tests) to beselected for use in the subsequent fabrication steps and to be mountedon the FFL correction substrate.

According to yet another aspect, a method of fabricating optical devicesincludes attaching a plurality of lens systems to a first side (i.e.,lens stack side) of a substrate composed of a material that issubstantially transparent to light of a predetermined wavelength orrange of wavelengths, providing a channel FFL correction layer on asecond side (i.e., sensor side) of the substrate; and removing selectedportions of the channel FFL correction layer so as to adjust forrespective focal length variations for at least some of the lenssystems. In some implementations, instead of removing selected portionsof the channel FFL correction layer so as to adjust for the respectivefocal length variations, one or more channel FFL correction layers areprovided where needed to correct for the focal length variations.

According to a further aspect, an apparatus includes a substrate havinga thickness that varies from one area of the substrate to another area.A plurality of singulated optical systems mounted over the substrate,wherein respective ones of the optical systems are disposed overdifferent areas of the substrate so as to provide focal lengthcorrections to at least some of the optical systems. The thicknesses ofthe different areas of the substrate can be provided, for example, so asto correct for variations in the focal lengths of the lens systems.

In another aspect, an optical module includes a substrate composed of amaterial that is transparent to light of a particular wavelength ofrange of wavelengths, and a plurality of lens systems attached over afirst side of the substrate, wherein each lens system has a respectiveoptical axis that intersects the substrate and corresponds to arespective optical channel in the module. The module includes aplurality of color filter layers disposed over different regions of thesubstrate, wherein the optical axis of each lens system intersects arespective one of the color filter layers. A spacer is disposed over thesubstrate between a respective pair of the color filter layers, and issubstantially non-transparent to light of the particular wavelength ofrange of wavelengths. A non-transparent (e.g., black) coating also canbe provided on a bottom surface of the substrate. The module includes achannel FFL correction layer, wherein the optical axis of at least oneof the lens systems intersects the channel FFL correction layer. Amodule FFL correction layer also can be provided. An image sensor isattached over a second side of the substrate.

Modules that include multiple optical channels as well as single channelmodules are described. In some cases, the thickness of a FFL correctionsubstrate can be adjusted, as needed, to provide FFL correction forindividual channels of a multi-channel module, and spacers can beprovided to provide FFL correction for the module as a whole. Insituations where the module includes only a single optical channel,spacers can be provided, and their height adjusted to provide a desiredFFL correction for the optical channel.

In some cases, instead of mounting singulated lens systems on a FFLcorrection substrate, an optics/spacer stack that includes multiple lensstacks is attached to the FFL correction substrate.

Other aspects, features and advantages will be apparent from thefollowing detailed description, the accompanying drawings and theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a method according to the present invention.

FIGS. 2 through 5 illustrate steps according to a first fabricationprocess.

FIG. 6 is an example of an optical module resulting from the firstfabrication process.

FIGS. 7 through 9 illustrate steps according to a second fabricationprocess.

FIGS. 10 and 11 illustrate examples of lens stack arrays on a FFLcorrection layer.

FIGS. 12 and 13 illustrated examples of FFL correction substrates thatinclude multiple FFL correction layers.

FIGS. 14 and 15 illustrate examples of lens stack arrays on FFLmulti-layer substrates.

FIGS. 16 and 17 illustrate examples of FFL correction substrates withadditional features.

FIGS. 18-24, 24A-24B, 25, 25A and 26-29 illustrate examples fabricationprocesses for making a sensor module that includes an array of lensstacks mounted on a FFL correction structure.

FIGS. 30 through 32 illustrate other examples of modules that include anarray of lens stacks with a FFL correction structure.

FIG. 33 illustrates an example of a single channel module according tothe present invention.

FIG. 34 illustrates a wafer-level technique for fabricating singlechannel modules.

FIGS. 35 through 38 illustrate a wafer-level technique for forming anoptics/spacer stack that includes multiple lens stacks.

DETAILED DESCRIPTION

As indicated by FIG. 1, a method of fabricating multiple optical modulescan include performing various steps at the wafer-level and incorporatesfeatures for correcting or otherwise adjusting focal length variationsof optical elements in each device. In the present context, a wafer canbe composed, for example, of a polymer material (e.g., a hardenablematerial such as a thermally or UV-curable polymer), a glass material, asemiconductor material, or a composite material comprising metals andpolymers or polymers and glass materials. In general, a wafer refers toa substantially disk- or plate-like shaped item, such that its dimensionin one direction (the z-direction or vertical direction) is small withrespect to its extension in the other two directions (the x- andy-directions or lateral directions). Multiple similar structures oritems can be arranged or provided on or in a (non-blank) wafer, forexample, on a rectangular grid. The wafer can have openings (i.e.,holes), and a wafer may even be free of material in a predominantportion of its lateral area.

As indicated by FIG. 1, multiple lens stacks can be fabricated, forexample, as part of a wafer level process (block 20). The lens stacksare separated from one another into individual lens stacks using dicingor other techniques (block 22). Some, or all, of the individual lensstacks then are mounted (e.g., attached) on a FFL correction substrate(block 24), which as explained below may include one or more FFLcorrection layers. The lens stacks can be mounted on the FFL correctionsubstrate, for example, using a bonding material such as glue or anepoxy resin. As part of the focal length variation correction oradjustment, the focal length of each lens stack can be measuredindividually. The focus length variations of the lens stacks areadjusted or corrected, for example, by micromachining the FFL correctionsubstrate (block 26). The micromachining step may include, for example,milling, drilling, laser ablation, etching and/or photolithography, aswell as other techniques. The individual lens stacks then can beseparated by dicing or some other process (block 28).

Although some of the foregoing steps are performed at the wafer level,mounting the individual lens stacks onto the FFL correction substrate(i.e., block 24) preferably is performed by placing individual (i.e.,singulated) lens stacks onto the FFL correction substrate. Such a methodcan be advantageous because it allows the individual lens stacks to betested prior to being mounted on the FFL correction substrate. Suchtesting allows only those lens stacks that satisfy specifiedrequirements (e.g., pass the optical or other tests) to be selected foruse in the subsequent fabrication steps and to be mounted on the FFLcorrection substrate. Nevertheless, one, two or more lens stacks may beplaced simultaneously on the FFL correction substrate.

FIGS. 2-5 illustrate an example of the method for fabricating multipleoptical modules. As shown in FIG. 2, a wafer-level process is used toform multiple lens stacks 40 by attaching multiple wafers to form awafer stack. In this example, each lens stack 40 includes pairs ofpassive optical components, such as plastic lenses 42A-42C and 44A-44C,arranged vertically one above another. Replication or other techniquescan be used to form lenses on respective surfaces of optics wafers 46A,46B which can be attached to one other by spacer wafers 48A, 48B. Thelenses can redirect light, for example, by refraction and/or bydiffraction. Thus, the lenses may be of generally convex shape or may bedifferently shaped, e.g., generally or partially concave. Each of lenses42A-42C and 44A-44C can have a nominal focal length; for example, lenses42A-42C can have the same first nominal focal length, and lenses 44A-44Ccan have the same second nominal focal length so that the overall focallength for each lens stack is about the same. However, in practicalapplications, the focal lengths of the lenses may deviate from theirrespective nominal focal lengths (e.g., as a result of manufacturinglimitations).

In the illustrated example, baffles 50 are provided around the openingat the top of each lens stack 40. Baffles 50 can prevent undesired lightfrom entering or leaving lens stack 40 at particular angles. Baffles 50can be composed, for example, of a material that substantiallyattenuates or blocks light at a particular wavelength or in a wavelengthrange.

The wafer stack of FIG. 2 is then diced into individual lens stacks 40,an example of which is illustrated in FIG. 3. The individual lens stacks40 then can be tested, and those lens stacks that satisfy any testingrequirements or other specifications are mounted on a FFL correctionsubstrate 52, as shown in FIG. 4. The optical axes for the opticalchannels are indicated by the dashed lines 41. FFL correction substrate52 can be composed, for example, of a transparent material (e.g., glass)with specified properties (e.g., to allow light of a particularwavelength or within a particular wavelength range to pass with littleor no attenuation).

The focal length of each lens stack 40 mounted on FFL correctionsubstrate 52 is measured, and the offset in relation to the image planeof the sensor is determined. Based on the resulting measurements, FFLcorrection substrate 52 is micro-machined (if needed) to correct thefocal length variation for each lens stack 40. The micro-machining caninclude forming a hole or other opening 54 in the sensor side of FFLcorrection substrate 52 below a particular lens stack 40. The depth ofholes 54 may vary and, in some cases, no hole may be needed for one ormore of the lens stacks 40 (e.g., if no correction or adjustment to thefocal length is needed). The holes provide air spaces which result inadjustments to the respective focal length variations for the lensstacks. The index of refraction of the material of substrate 52 isdifferent from (e.g., greater than) the index of refraction of vacuum orair in the holes 54. Thus, by adjusting the depths of each hole 54 independence of the deviation of the focal length of the associatedoptical components from the respective nominal focal length, deviationscan be compensated, at least to some degree. The depths of the holes canbe selected, for example, so that the resulting focal lengths of all thelens stacks are substantially the same as one another. Alternatively,the FFL correction layer can be adjusted by photolithographictechniques, which can be particularly helpful when several layers of FFLcorrection layers are used (see FIGS. 26 and 27). This can beparticularly useful, for example, for fabrication of optical devicesthat include an array of lenses.

After mounting lens stacks 40 on FFL correction substrate 52, the gapsbetween adjacent lens stacks can be filled (or partially filled) with anon-transparent material 56 (e.g., black epoxy) so that each lens stackis surrounded by non-transparent walls that help prevent stray lightfrom entering the lens stack during subsequent use. FFL correctionsubstrate 52 (and non-transparent material 56, if present) then is dicedor otherwise separated to form individual optical modules each of whichincludes a lens stack 40 with FFL correction. An example of such anoptical module 60 is illustrated in FIG. 6.

In the example of FIGS. 2-6, each lens stack 40 includes an array oflenses aligned vertically with one another. In other implementations,the lens stack may include a different number of lenses, different typesof lenses, or a different arrangement of lenses. Thus, lens stack 40 isan example of a lens system that can be incorporated into optical module60. The lens system can include one or more lenses or other passiveoptical elements, which may be focused or non-focused.

In the example of FIGS. 2-6, lens stacks 40 are fabricated using awafer-level process that includes stacking multiple substrate wafers oneatop the other to form a wafer stack that subsequently is diced toprovide the individual lens stacks. In other implementations, the lensstacks can be made using an injection molding technique. For example, asshown in FIGS. 7 and 8, one or more plastic lenses 70, 72 made byinjection molding are introduced into a lens barrel or other lens holder74 to form a lens system, in this case a lens stack 80. Lens barrel 74can be formed, for example, of non-transparent material such as athermoplastic material (e.g., polycarbonate with fillers or a liquidcrystal polymer with glass fibers) and includes an opening 76 at its topend to allow light to enter or exit.

Lens stacks 80 then can be mounted on a FFL correction substrate 52 in amanner similar to that described above in connection with FIG. 4 (i.e.,individual singulated lens stacks 80 are mounted on FFL correctionsubstrate 52). The focal length of each lens stack 80 mounted on FFLcorrection substrate 52 is measured, and based on the resultingmeasurements, FFL correction substrate 52 is micro-machined (if needed)to adjust the focal length variation for each lens stack 80. Asdescribed above in connection with FIG. 5, the micro-machining caninclude forming a hole 54 in the sensor-side surface of FFL correctionsubstrate 52 below a particular lens stack 80 (see FIG. 9). The depth ofholes 54 may vary and, in some cases, no hole may be needed for one ormore of the lens stacks 80 (e.g., if no correction or adjustment to thefocal length is needed). FFL correction substrate 52 then can be dicedor otherwise separated to form individual optical modules each of whichincludes a lens stack 80 with FFL correction.

In the foregoing illustrated examples, each module includes a singlelens stack. However, in other implementations, each module can includetwo or more lens stacks. In some cases, each module includes an array oflens stacks (e.g., a 2×2 array, a 3×3 array, a 4×4 array, or a M×Narray, where M and N are positive integers that may be the same ordifferent from one another). In such implementations, M×N arrays of lensstacks can be attached to a FFL correction substrate 52 as illustrated,for example, in FIGS. 10 and 11. FIG. 10, for example, illustrates M×Narrays of lens stacks 40 that were manufactured in a wafer-leveltechnique, whereas FIG. 11 illustrates M×N arrays of lens stacks 40formed by an injection molding technique. After dicing FFL correctionlayer 52, each module will include multiple lens stacks alignedside-by-side.

FFL correction substrate 52 can be composed of a single layer as in theexamples of FIGS. 5 and 9. However, in other implementations, FFLcorrection substrate 52 can include multiple layers of differentmaterials depending on the desired optical properties for the resultingoptical modules. For example, FIG. 12 illustrates an example in whichthe FFL correction substrate is composed of a bottom layer 52A and a toplayer 52B. In the illustrated example, holes for the FFL correction areformed in bottom layer 52A. FIG. 13 illustrates an example in which theFFL correction layer includes a bottom layer 52C, a middle layer 52D anda top layer 52E. In the illustrated example, holes 54 for the FFLcorrection are formed in bottom layer 52C. The various FFL layers can becomposed, for example, of glass materials and/or polymer materials. M×Narrays of lens stacks also can be mounted on multi-layer FFL correctionsubstrates. Examples are illustrated in FIGS. 14 and 15, which show,respectively, M×N arrays of lens stacks 40 on an FFL correctionsubstrate 52 composed of multiple layers 52A, 52B of differentmaterials. In some implementations, the FFL correction substrate may becomposed of more than two different layers.

In some implementations, one or more color filters and/or infra-red (IR)filters can be provided on FFL correction substrate 52 to obtain desiredoptical properties for the resulting optical modules. Color filters caninclude, for example, monochromous red, green and blue filters, or Bayerpattern filters. Also, in some implementations, IR filters or neutraldensity filters can be provided. An example is illustrated in FIG. 16,which includes an IR filter layer 90 on the lens stack side of FFLcorrection substrate 52 and color filters 92 on the IR filter layer.Color filters are disposed at locations that correspond to opticalchannels for each lens stacks (e.g., lens stacks 40 or 80). Thus, a lensstack 40 (or 80) can be mounted, for example, on or over each of thecolor filters 92.

Furthermore, in some implementations, each optical module includesmultiple lens stacks. For example, a first lens stack may be alignedwith a light emitting element (e.g., a LED), and a second lens stack maybe aligned with a light detecting element (e.g., a photodiode). In thatcase, the color filters 92 on FFL correction substrate 52 may havedifferent optical properties from one another, and a cross channel straylight reduction feature can be provided between the two channels. Asillustrated in FIG. 16, cross channel stray light reduction can beimplemented by a black spacer 96 atop a black coating layer 94. In someimplementations, black spacer 96 is applied directly to FFL correctionsubstrate 52 or IR filter layer 90 (i.e., without black coating layer94). Black spacer 96 and black coating layer 94 are substantiallynon-transparent to light over a predetermined range of wavelengths(e.g., in the visible part of the spectrum, the IR part of the spectrum,and/or the UV part of the spectrum). Suitable coating techniquesinclude, for example, spin coating, spraying and sputtering. Suchcoating techniques can be used to provide black coating layer 94, IRfilter layer 90, and/or color filter coating 92. Multiple lens stacks 40(or 80) can be mounted on a single FFL correction substrate 52, whichthen can be micro-machined to adjust the respective focal lengthvariations. FFL correction substrate 52 then can be diced at theappropriate locations so that each module includes a pair of lensstacks, rather than just a single lens stack.

In some implementations, a black (i.e., non-transparent) coating can beadded to the bottom (i.e., sensor-side) surface of FFL correctionsubstrate, to the bottom surface of one or more of the FFL correctionlayers, and/or between adjacent FFL correction layers. FIG. 17illustrates an example of a glass FFL correction substrate 52 that hasan IR filter 90, color filters 92, and a black spacer 96 atop a blackcoating layer 94 for cross channel stray light reduction on the lensstack side of FFL correction substrate 52. The sensor side of substrate52 includes a channel FFL correction layer 100 and a module FFLcorrection layer 102. Channel FFL correction layer 100 can provide FFLcorrection or adjustment that differs for the two channels (i.e., C1 andC2). Module FFL correction layer 102 can provide an additional FFLcorrection or other adjustment that applies equally to all the opticalchannels. Black coating layers 104 can be provided to help reduce straylight in the optical module. Coating techniques (e.g., spin coating,spraying and sputtering) can be used to provide black coating layers 104and/or channel FFL correction layer 100. In a particular implementation,the thickness of the FFL correction layers is approximately as follows:400 μm for FFL correction substrate 52, 25 μm for FFL correction layer100, and 150 μm for FFL correction layer 102.

FIGS. 18 through 29 illustrate an example fabrication process for makinga sensor module that includes an array of lens stacks mounted on a FFLcorrection structure with various features similar to those of FIG. 17.As shown in FIG. 18, a glass or other substrate 202 serves as a firstFFL correction substrate. Dashed vertical lines 204 indicate thelocations of optical axes for optical channels. An IR filter layer 206can be coated on the lens stack side of substrate 202 (i.e., the side onwhich the lens stacks are to be mounted). As shown in FIG. 19, theentire sensor side of FFL substrate 202 (i.e., the side on which thesensor is to be attached) is coated with a black coating 208 (i.e., amaterial that absorbs all or a substantial amount of light impinging onits surface or that is substantially non-transparent to a particularwavelength or range of wavelengths). Coating 208 can help reduce opticalcross-talk or interference caused by stray light. Photolithographictechniques can be used to remove portions of coating 208 to provideopenings 210 in the vicinity of the optical channels as shown in FIG.20.

As illustrated in FIG. 21, the lens stack side of FFL substrate 202 iscoated with a first color filter layer 212. Next, portions of firstcolor filter layer 212 are removed, for example, by photolithographictechniques, except on areas over selected ones of channel openings 210(see FIG. 22). The foregoing steps are repeated for a second colorfilter layer 214, such that, as shown in FIG. 23 each channel opening210 is covered by one of the first or second color filter layers 212,214. In the illustrated example, areas above channel openings 210 arecovered alternately by either the first color filter layer 212 or thesecond color filter layer 214. The first and second color filter layersallow selected wavelengths or wavelength ranges (e.g., red, green orblue) to pass through. In some implementations, more than two differentcolor filters are applied. For example, in some cases, three colorfilters are applied so as to obtain red, green and blue channels.

As illustrated by FIG. 24, black spacers 216 (i.e., composed of amaterial that absorbs all or a substantial amount of light impinging ontheir surface or that is non-transparent to substantially all the lightin a particular wavelength or range of wavelengths) are provided on thelens stack side of FFL substrate 202 between pairs of adjacent colorfilters 212, 214. Black spacers 216, which can be formed for example byvacuum injection techniques, can help reduce cross channel stray light.In this case, a FFL correction wafer can be placed on a vacuum chuck,and a PDMS tool with spacer sections is brought into contact with theFFL correction wafer. A vacuum is applied, and non-transparent, curableepoxy material is injected into the tool to form the spacers on the FFLcorrection wafer. The epoxy material can be hardened by applying UVradiation. Alternatively, embossing techniques can be used to form blackspacers 216. In some implementations, additional black spacers 216A canbe provided on the sides of color filter 212, 214 such that the blackspacers 216A surround the color filters in a grid-like manner as shownin FIGS. 24A and 24B. The size and position of black spacers 216 maydepend on the dimensions of the overlying lens stacks that are to beplaced on FFL substrate 202.

As shown in FIG. 25, individual lens stacks or M×N arrays 218 of lensstacks are attached over the lens stack side of FFL substrate 202. If IRfilter layer 206 is not present, then M×N arrays 218 can be attacheddirectly to the lens stack side of FFL substrate 202. Otherwise, M×Narrays 218 can be attached to the upper surface of IR filter layer 206.If black spacers 216 surround the color filters as in FIG. 24A, then thelens stack can be mounted directly on the black spacers 216 as shown inFIG. 25A.

Next, the FFL is measured for each lens stack in M×N arrays 218. Achannel FFL correction layer 220 then is attached or applied (e.g., bycoating techniques such as spin coating, spraying or sputtering) to thesensor side of FFL substrate 202, as illustrated in FIG. 26. Channel FFLlayer 220 can be composed, for example, of a glass material and/orpolymer material. Based on the FFL measurement for each lens stack,photolithographic techniques are used to remove portions of channel FFLcorrection layer 220 below the various lens stacks so as to achievedesired FFL values for the lens stacks. Since the lens stacks may havedifferent FFL values, different amounts of channel FFL correction layer220 may be needed to achieve corrected FFL values for the various lensstacks (see FIG. 27). For some lens stacks, no FFL correction may beneeded, in which case channel FFL correction layer 220 can be removed inits entirety in the areas below those particular lens stacks. In othercases, a portion of channel FFL correction layer 220 may be removed inthe area below a particular lens stack. In yet other cases, no portionof channel FFL correction layer 220 may be removed below a particularlens stack. Thus, depending on the implementation, channel FFLcorrection layer 220 may be present for all of the lens system or onlysome of the lens systems. Furthermore, the thickness of the finalchannel FFL correction layer 220 may vary from one lens system to thenext, depending on the amount of FFL correction needed for each lenssystem.

Next, as shown in FIG. 28, spacers 222 can be attached, for example, atthe sensor side of FFL substrate 202 (e.g., to the lower surface ofblack coating 208), which can increase the stability of the module. Insome implementations, spacers 222 are provided by a vacuum injectiontechnique. Spacers 222 can serve as a module FFL correction layer. Theheight of the spacers 222 can be adjusted separately for each module(e.g., each 2×2 array of lens stacks) to compensate for the FFLvariation. Such adjustments can be performed, for example, usingmicromachining techniques. The individual modules can be separated, forexample, by dicing along dicing lines 224.

An image sensor 226 then can be attached to the lower side of spacers222, as shown in FIG. 29. Image sensor 226 can include, for example,multiple light emitting and/or light sensing elements aligned,respectively, with different optical channels 204 in the module. Aboveeach lens system is a respective opening 228 that is substantiallyaligned with the optical axis 204 of a particular one of the lenssystems and that allows light to enter or exit the module. The foregoingtechniques can provide a module with one or more lens stacks having FFLvalues that are adjusted to achieve effective desired values using a FFLcorrection structure.

In some implementations, the various steps of FIGS. 18-29 may beperformed in a different order. For example, it is possible to processcolor filters 212, 214 and black spacers 216 before applying blackcoating 208. It is also possible to measure the FFL of the lens stacksseparately before they are attached to the FFL correction structure, andto proceed with subsequent processing steps (e.g., as in FIG. 26, 27,28, 30 or 31) without the lens stack attached. In some cases, some ofthe steps may be omitted or additional steps may be added. Depending onthe implementation, coatings 206, 208, 212, 214 can be applied to thelens side or the sensor side of FFL correction substrate 202 or channelFFL correction layer 220.

Depending on the amount of FFL compensation required for a particularlens stack, multiple channel FFL correction layers 220A, 220B can beprovided. An example is illustrated in FIG. 30, which shows the use of afirst channel FFL correction layer for some of the lens stacks, and theuse of first and second channel FFL correction layers 220A, 220B forother of the lens stacks.

Instead of using photolithographic techniques to remove portions ofchannel FFL correction layer 220 (see the description above inconnection with FIGS. 26 and 27), micromachining techniques can be usedto remove portions of channel FFL correction layer 220 (see FIG. 31). Inthat case, FFL correction spacers 222 for the modules can be attached tochannel FFL correction layer 220 (see FIG. 31), instead of beingattached to black coating 208.

In the foregoing examples, channel FFL correction layer 220 is attachedat the sensor side of FFL correction substrate 202 (i.e., on the imagesensor side). In some implementations, a channel FFL correction layer220 can be attached to the lens stack side of FFL correction substrate202. For example, as illustrated in FIG. 32, channel FFL correctionlayer 220 can be provided over color filter layers 212, 214 in theparticular optical channels for those lens stacks requiring FFLcorrection. Channel FFL correction layer 220 can be added, for example,prior to mounting the lens stacks. Photolithographic techniques can beused to form channel FFL correction layer 220. Such techniques can beparticularly useful, for example, if the lens stacks display arelatively uniform and reproducible FFL variation.

As described above in connection with FIG. 28 for modules that includemultiple optical channels, FFL correction layers 202 can be added, asneeded, to provide FFL correction for individual channels, and spacers222 can be added to provide FFL correction for the module as a whole. Insituations where the module includes only a single optical channel(rather than multiple channels), spacers can be attached to thetransparent substrate 202, and their height adjusted to provide adesired FFL correction for the optical channel. As the module includesonly a single optical channel, there is no need to include separate FFLcorrection layers 220. An example of such a module is illustrated inFIG. 33, which shows lens stack 40 attached to a transparent cover 202by way of a first spacer 216A. The sensor side of the transparent cover202 is attached, by way of a second spacer 222, to an image sensor 238that includes a light detecting element (e.g., a photodiode) 240. Inthis and the other implementations described above, the spacers 216A,222 can be, for example, ring shaped and can be formed, for example, byvacuum injection. The image sensor 238 is mounted on a substrate 242.

The single channel module of FIG. 33 can be fabricated, for example,using a wafer-level technique. As shown in FIG. 34, first spacers 352are attached to one side of a transparent wafer 354, and second spacers356 are attached to the second side of the transparent wafer 404.Spacers wafers can be used to provide the first and second spacers 352,356. In some implementations, the spacers 352, 356 are formed on thetransparent wafer 354 by a vacuum injection technique. The transparentwafer 354 can be composed, for example, of glass or polymer material,whereas the spacers 352, 356 can be composed, for example, of anon-transparent material. Singulated injection molded lens stacks 40 areattached to the first spacers 352. The FFL of each lens stack 40 then ismeasured and, if needed, the height of the spacers 356 where the lensstack 40 is attached can be adjusted to provide FFL correction for theoptical channel. The height of the spacers 356 can be adjusted, forexample, by micromachining or other techniques. The sensor side spacerwafer 356 then is attached to respective image sensors 238 mounted on asubstrate wafer (e.g., a printed circuit board wafer) 358. The resultingstack can be separated (e.g., by dicing) to obtain single channelmodules.

In the foregoing examples, mounting the lens stacks on the FFLcorrection substrate preferably is performed by placing individual(i.e., singulated) lens stacks onto the FFL correction substrate.However, in some implementations, instead of placing singulated lensstacks on the FFL correction substrate, a stack 302 of transparentoptics wafers 304, each of which has multiple lenses 306, can be placedon a FFL correction substrate 308 (see FIG. 35). The stack 302 of opticswafers 304 can include non-transparent spacers 310A, 310B that separatethe optics wafers 304 from one another and from the FFL correctionsubstrate 308.

The spacer/optics stack 302 can be attached to the FFL correctionsubstrate 308 using, for example, a thermally stable adhesive. In orderto prevent stray light, openings such as trenches 312 are formed betweenthe lens stacks and subsequently are filled with non-transparentmaterial (see FIG. 36). Trenches 312 should extend entirely through thethickness of both wafers 304 and, preferably, should extend at leastpartially into lower spacers 310B. In some cases, the trenches 312 canextend to the upper surface of the FFL correction substrate 308.Trenches 312 can be formed, for example, by dicing, micromachining orlaser cutting techniques. As explained below, trenches 312 subsequentlycan be filled with a non-transparent material so as to provide anon-transparent layer on the sidewalls of the various portions of thetransparent wafers 304.

As shown in FIG. 37, a vacuum injection PDMS tool 314 is placed over thespacer/optics stack 302 to facilitate filling trenches 312 with anon-transparent material (e.g., epoxy with carbon black). A vacuum chuck316 is provided below and around the spacer/optics stack 302 so as toapply a vacuum between the vacuum injection tool 314 and the FFLcorrection substrate 308. The non-transparent material can be injectedinto an inlet 318 in the vacuum chuck 316. A vacuum pump 320 near anoutlet of the vacuum chuck 316 facilitates flow of the injectednon-transparent material. Examples of the non-transparent materialinclude UV- or thermally-curing epoxies (or other polymers) containingcarbon black (or another dark pigment) or an inorganic filler or a dye.In some implementations, the additive is embedded in the epoxy (or otherpolymer).

After filling trenches 312 with the non-transparent material undervacuum, the material is hardened (e.g., by UV or thermal curing), andthe tool 314 is removed from the spacer/optics stack 302. The result, asshown in FIG. 38, is that non-transparent regions 322 (e.g., epoxy withcarbon black) are formed between adjacent portions of the transparentoptics wafers 304. The top portion of the non-transparent regions 322can be substantially flush with the exterior surface of the variousportions of the transparent optics wafers 304 and can be composed of thesame non-transparent material or a different non-transparent material asspacers 310A, 310B. In some implementations, a baffle wafer composed ofa non-transparent material is attached over the optics/spacer stack 302.In other implementations, the baffle wafer can be omitted.

After forming the non-transparent regions 322 and removing the vacuuminjection tool 314, the FFL correction substrate 308 can be processed asdescribed above. Thus, for example, a method of fabricating opticaldevices can include attaching, over a transparent FFL correctionsubstrate, an optics/spacer stack that includes a plurality of lenssystems. In some cases, openings such as trenches are formed throughportions of the optics/spacer stack that separate the lens systems fromone another, and the openings then are filled with a non-transparentmaterial. The thickness of the substrate can be adjusted below at leastsome of the lens systems to provide respective focal length correctionsfor the lens systems. Adjusting the thickness of the substrate mayinclude removing selected portions of the FFL correction substrate oradding one or more layers below at least some of the lens systems so asto correct for variations in the focal lengths of the lens systems.Subsequently, the FFL correction substrate can be separated into aplurality of optical modules, each of which includes one or more of thelens systems mounted over a portion of the FFL correction substrate. Thesides of the resulting modules, including the sides of the transparentsubstrates on which the lenses are formed, are covered bynon-transparent material, which can help reduce stray light fromentering the modules.

Other implementations are within the scope of the claims.

What is claimed is:
 1. A method of fabricating optical devices, themethod comprising: providing first spacers on a first side of a wafercomposed of a material that is substantially transparent to light of apredetermined wavelength or range of wavelengths; providing secondspacers on a second side of the wafer, the first and second sides beingopposite sides of the wafer; attaching a plurality of singulated lenssystems to the first spacers, wherein the singulated lens systems arephysically unattached from one another at least at a time just prior toattaching the singulated lens systems to the first spacers; adjusting aheight of at least part of the second spacers to provide for FFLcorrection for one or more optical channels; subsequently attaching thesecond spacers to respective image sensors, wherein each of the imagesensors includes a light detecting element such that the light detectingelement is laterally encircled entirely by a respective one of thesecond spacers after the second spacers are attached to the imagesensors, wherein a plane parallel to the wafer intersects both the lightdetecting element and the second spacers: separating the wafer so as toform single channel modules each of which includes a singulated lenssystem disposed over an image sensor.
 2. The method of claim 1 furtherincluding measuring the FFL of the lens systems.
 3. The method of claim2 further including adjusting a height of at least some of the secondspacers, based on results of the measuring, to provide for FFLcorrection for one or more optical channels.
 4. The method of claim 3wherein adjusting a height includes micromachining.
 5. The method ofclaim 1 including forming the first spacers and the second spacers byvacuum injection.
 6. The method of claim 1 wherein the singulated lenssystems are injection molded lens stacks.
 7. The method of claim 1wherein the wafer is composed of a glass or polymer material.
 8. Themethod of claim 1 wherein the first and second spacers are composed of amaterial that is substantially non-transparent to light of thepredetermined wavelength or range of wavelengths.
 9. The method of claim1 wherein each of the lens systems includes a plurality of lensesstacked one over the other.
 10. The method of claim 1 wherein each ofthe lens systems includes a plurality of lens arrays stacked one overthe other.
 11. A method of fabricating optical devices, the methodcomprising: providing a first spacer wafer on a first side of atransparent wafer composed of a material that is substantiallytransparent to light of a predetermined wavelength or range ofwavelengths; providing a second spacer wafer on a second side of thetransparent wafer, the first and second sides being opposite sides ofthe transparent wafer; attaching a plurality of singulated lens systemsto the first spacer wafer, the singulated lens systems being laterallyspaced from one another, and the singulated lens systems beingphysically unattached from one another at least at a time just prior toattaching the singulated lens systems to the first spacer wafer;adjusting a height of at least part of the second spacer wafer toprovide for FFL correction for one or more optical channels;subsequently attaching the second spacer wafer to image sensorslaterally spaced from one another, wherein each of the image sensorsincludes a light detecting element such that the light detecting elementis laterally encircled entirely by the second spacer wafer after thesecond spacer wafer is attached to the image sensors, wherein a planeparallel to the transparent wafer intersects both the light detectingelements and the second spacer wafer; and separating the wafers so as toform single channel modules each of which includes a singulated lenssystem disposed over an image sensor.
 12. The method of claim 11 furtherincluding measuring the FFL of the lens systems.
 13. The method of claim12 further including adjusting a height of at least part of the secondspacer wafer, based on results of the measuring, to provide for FFLcorrection for one or more optical channels.
 14. The method of claim 13wherein adjusting a height includes micromachining.
 15. The method ofclaim 11 wherein the singulated lens systems are injection molded lensstacks.
 16. The method of claim 11 wherein the transparent wafer iscomposed of a glass or polymer material.
 17. The method of claim 11wherein the first and second spacer wafers are composed of a materialthat is substantially non-transparent to light of the predeterminedwavelength or range of wavelengths.
 18. The method of claim 11 whereineach of the lens systems includes a plurality of lenses stacked one overthe other.
 19. The method of claim 11 wherein each of the lens systemsincludes a plurality of lens arrays stacked one over the other.